The present invention relates to shutoff valves for gas storage containers; more particularly, to such valves for storage of oxygen for emergency breathing aboard aircraft; and most particularly, to such a valve having an electric-powered indicator for showing whether the valve is open or closed independent of the pressure behind the valve.
Oxygen gas is routinely available for emergency or high-altitude breathing by passengers on aircraft. Typically, oxygen is stored at high pressure in storage tanks mounted remotely in the aircraft from intended points of use. Each tank has a manually-operable outlet valve which is connected by tubing to a respirator or other breathing device at each point of use. Prior to designated periods, such as during flight, the tank valve is placed in the open position by unscrewing the valve stem to retract the poppet from the valve seat so that oxygen is immediately available where needed simply by actuating a respirator. In the prior art, an annunciator, typically a status light located in the cockpit of the aircraft, is connected to a pressure sensor opening into the tubing to indicate that the tubing and respirator(s) are pressurized and ready for service.
In the prior art arrangement, one must infer from a positive pressure indication by the annunciator that the tank valve is open; there is no redundant indicator on the tank valve itself. Experience has shown, however, that it is possible to trap pressure in the tubing if the tank valve is opened and then reclosed, as may occur during preflight operations, thus giving a false positive indication that a flow of oxygen is available on demand. In many aircraft, the tank itself is not accessible to persons on board the aircraft during flight, so such an error is highly dangerous. It is believed that a recent notorious flying fatality was caused by this or a closely-related scenario.
U.S. Pat. No. 4,518,008 discloses a supervisory electrical switch mounted on a quarter-turn hand valve to indicate that the valve is open. The switch is activated by a cam mounted on the valve stem and rotatable therewith. This mechanism is not suitable for use on a multi-turn hand valve such as is used on oxygen tanks.
U.S. Pat. No. 4,721,131 discloses a supervisory optical switch for indicating a hand valve is open. The switch is activated by a lever that is moved by a follower driven axially of the valve by the valve stem. This mechanism is not suited to an electrical annunciation system such as is commonly used on aircraft.
U.S. Pat. No. 4,665,386 discloses a valve position-annuciating device wherein an auxiliary knob disposed on the valve-opening knob carries a permanent magnet to operate a position-sensitive magnetic switch. This mechanism requires a critical positioning of the magnet with respect to the switch.
U.S. Pat. No. 5,277,223 discloses a valve position transmitter than shows continuously the position or degree of openness of a valve.
U.S. Pat. No. 4,046,364 discloses a torque limiter including a sprag clutch for limiting the force of the threadedly moveable jaw of a vise.
U.S. Pat. No. 4,988,078 discloses a poppet valve having a seat machined into a body element.
What is needed is a direct and positive annunciation of the position, open or closed, of the tank valve on an oxygen tank for breathing in an aircraft.
In addition, what is needed is a simplified valve having fewer parts and a stem torque limiter, thus reducing manufacturing cost, improving reliability, and reducing the potential for valve seat damage.
It is the primary object of the invention to provide an improved aircraft safety system wherein the open position of a remotely located improved and simplified aircraft oxygen tank valve can be assured in the cockpit prior to takeoff.
The invention is directed to an improved manually-operable outlet valve for a tank of pressurized gas, especially a tank in a pressurized breathing oxygen system in an aircraft. The valve has a valve body conventionally attachable to a standard oxygen tank. A rotatable valve stem is conventionally disposed within a threaded port in the valve body to open and close a poppet valve therein. The poppet mates with a seat machined in the valve body to effect an openable and closable valve seal therein. The poppet is provided with a torque limiter comprising a stack of Belville washers disposed on the valve stem. A lever and an electrical microswitch are mounted on the valve body. The valve stem is provided with a handle, for grasping as by an operator to open and close the valve, and a collar surrounding the stem for riding axially with the valve stem during actuation of the valve. The collar intercepts and actuates the lever during axial travel of the collar, and the lever actuates the microswitch from an open to closed position or the reverse, the switch being in a first state at one extreme of collar travel and in the opposite state at the opposite extreme of collar travel. The microswitch is attached to an electrical connector for connection to a circuit including an annunciator in the cockpit of the aircraft, the microswitch and annunciator preferably being wired such that the annunciator is illuminated when the valve is open.